Electromechanical transformation device and method for manufacturing the same

ABSTRACT

An electromechanical transformation device comprises an alkaline niobate piezoelectric ceramic composition and a rigid body adhered onto the major surface of the piezoelectric ceramic composition. The piezoelectric ceramic composition is made of crystal structures such as orthorhombic crystals formed at the side where the temperature is lower than the orthorhombic-to-tetragonal phase transition temperature, tetragonal crystals formed at the side where the temperature is higher than the orthorhombic-to-tetragonal phase transition temperature as well as at the side where the temperature is lower than the tetragonal-to-cubic phase transition temperature, and the cubic crystals formed at the side where the temperature is higher than the tetragonal-to-cubic phase transition temperature. Young&#39;s modulus of the rigid body is 60 GPa or more and the volume percent of the piezoelectric ceramic composition existing within a range where the distance from the adhesion point of the piezoelectric ceramic composition and the rigid body is 40% or more.

TECHNICAL FIELD

This invention relates to an electromechanical-transformation devicecomprising crystal structures that include an orthorhombic crystalformed at the side where the temperature is lower than theorthorhombic-to-tetragonal-phase transition temperature, a tetragonalcrystal formed at the side where the temperature is higher than theorthorhombic-to-tetragonal-phase transition temperature, and at the sidewhere the temperature is lower than the tetragonal-to-cubic-phasetransition temperature, and a cubic crystal formed at the side where thetemperature is higher than the tetragonal-to-cubic-phase transitiontemperature, and to a method for manufacturing the same device.

TECHNICAL BACKGROUND

A piezoelectric ceramic composition is nowadays used for anelectromechanical transformation device such as actuators,ultrasonic-sensors, ultrasonic-transducers or the like. Apiezoelectric-ceramic composition showing an excellent piezoelectricproperty contains a lead compound such as lead zirconate titanate (PZT)or the like. However, that is a cause for concern regarding the negativeaffect that it has on the environment. Therefore, apiezoelectric-ceramic composition that is free of such a lead-compoundis now attracting attention and is being researched and developed. Asdisclosed below in Patent Reference One, thepotassium-sodium-niobate-system piezoelectric-ceramic composition isjust such a composition that is free of lead and yet has an excellentpiezoelectric property of a relatively high electromechanical-couplingcoefficient as well as a relatively high Curie temperature Tc, so thatit can appropriately be used under high temperatures.

The type of piezoelectric-ceramic composition showing an excellentpiezoelectric property that is nowadays used in the making ofelectromechanical-transformation devices such as actuators,ultrasonic-sensors, ultrasonic-transducers or the like contains a leadcompound such as lead zirconate titanate (PZT) or the like. However,that type of piezoelectric-ceramic composition is a cause for concernregarding the negative affect that it has on the environment. Therefore,a piezoelectric-ceramic composition that is free of such a lead compoundis now attracting attention and is being researched and developed. Asdisclosed below, in Patent Reference One, thepotassium-sodium-niobate-system piezoelectric-ceramic composition isjust such a composition that is free of lead and yet has an excellentpiezoelectric property of a relatively high electromechanical-couplingcoefficient, as well as a relatively high Curie temperature Tc, so thatsaid composition can appropriately be used under high temperatures.

The potassium-sodium-niobate-system piezoelectric-ceramic compositionincorporates a crystalline-phase of a perovskite structure that is shownas composition-formula ABO₃. Although the perovskite structure dependson this type of composition, the piezoelectric-ceramic compositionincorporating the potassium-sodium-niobate-system material reveals thetetragonal-to-cubic-phase transition temperature Tc to be about 300 to400 degrees Celsius and the orthorhombic-to-tetragonal-phase transitiontemperature To-t to be about −30 degrees to +100 degrees Celsius. Ifsuch a piezoelectric-ceramic composition is used in the making of anelectromechanical-transformation device, then polarization is typicallydone by applying a high electric field within the temperature-rangerequired to form the tetragonal-crystal to get the piezoelectricproperty.

PRIOR ART DOCUMENTS

-   Patent Document One: JP-A-2008-162889

DISCLOSURE OF THE INVENTION Problems to be Resolved by the Invention

If an electromechanical-transformation device is used under thetemperature exceeding the tetragonal-to-cubic-phase transitiontemperature Tc, polarization will be disordered, and the piezoelectricproperty will be lost (i.e. depolarization will occur). Depolarizationmoderately occurs at a temperature ranging from 100 to 150 degreesCelsius lower than the tetragonal-to-cubic-phase transition temperatureTc. Thus, to design an electromechanical-transformation device properly,it is necessary to set the upper-limit operating temperature of thedevice at 100 degrees or lower than the tetragonal-to-cubic-phasetransition temperature Tc. Yet, the piezoelectric property of such anelectromechanical-transformation device deteriorates over time perchanges in the orthorhombic-to-tetragonal-phase transition temperatureTo-t. Therefore, to keep long-term product reliability, it is betterthat the orthorhombic-to-tetragonal-phase transition temperature To-tnot be within the electromechanical-transformation-device operatingtemperature.

An ultrasonic flow meter must be used to measure the flow-volume of thechemical-solution circulation-line that is integrated in thesemiconductor manufacturing equipment in an inhospitable environmentunder an operating temperature ranging from 0 to 200 degrees Celsius. Tosatisfy long-term product liability of the ultrasonic sensor(electromechanical-transformation device) to be used in such a flowmeter, a piezoelectric-ceramic composition that has, for instance, atetragonal-to-cubic-phase transition temperature Tc of 340 degrees C. orhigher and an orthorhombic-to-tetragonal-phase transition temperatureTo-t of minus 20 degrees Celsius or lower, must be used. To achieve apotassium-sodium-niobate-system piezoelectric-ceramic composition thatsatisfies the condition of the phase-transition temperature and has apreferable piezoelectric property, modifications of such a compositionare currently underway. However, such a suitable composition has yet tobe developed.

This invention has achieved, in light of the aforementioned problems, inproviding an electromechanical-transformation device of which thepiezoelectric property is unlikely to deteriorate over time, even ifchanges in temperature should occur, including changes in theorthorhombic-to-tetragonal-phase transition temperature. Also, apreferable method for manufacturing thiselectromechanical-transformation device, as described above, has beenprovided.

Means of Solving the Problems

To solve the aforementioned problems, the first aspect of this inventionrefers to an electromechanical-transformation device comprising crystalstructures that include an orthorhombic crystal formed at the side wherethe temperature is lower than the orthorhombic-to-tetragonal-phasetransition temperature, a tetragonal crystal formed at the side wherethe temperature is higher than the orthorhombic-to-tetragonal-phasetransition temperature, and at the side where the temperature is lowerthan the tetragonal-to-cubic-phase transition temperature, and a cubiccrystal formed at the side where the temperature is higher than thetetragonal-to-cubic-phase transition temperature, and wherein theelectromechanical-transformation device comprises apiezoelectric-ceramic composition of which the volume-percentage, beingwithin the range of which the distance from the point of attachment ofthe rigid body to the piezoelectric-ceramic composition is two mm orless, is 40% or more as compared to the whole piezoelectric-ceramiccomposition, and wherein the electromechanical-transformation devicecomprises a rigid body having a Young's modulus of 60 GPa or more, whichis directly adhered to the major surface of a piezoelectric-ceramiccomposition or indirectly to the major surface by the intermediaryelectrodes.

According to the first aspect of this invention, the relatively hardrigid body, having a Young's modulus of 60 GPa or more, is adhered tothe major surface of the piezoelectric-ceramic composition or to theelectrodes formed on the major surface of said composition. The adhesionarea of the hard rigid body is sufficiently secured such that thepercentage in mass of the piezoelectric-ceramic composition, beingwithin the range of two mm or less from the point of attachment betweenthe piezoelectric-ceramic composition and the rigid body, is 40% ormore. As such, the rigid body adhered to the piezoelectric-ceramiccomposition makes it difficult to create the phase-transition of thecrystal structures of the piezoelectric-ceramic composition even if achange should occur in the orthorhombic-to-tetragonal-phase transitiontemperature. Even when a phase-transition of the crystal structures ofthe piezoelectric-ceramic composition occurs, then lattice-distortion ofthe crystal structures will occur. Then, expansion or contraction of thepiezoelectric-ceramic composition due to the variation in temperature(i.e. the linear-thermal expansion-coefficient) becomes extremelygreater compared to that of the rigid body. Of this invention, byadhering the rigid body to the piezoelectric-ceramic composition, theexternal force will work in the direction where the lattice-distortiondone by the phase-transition is controlled. Thus, phase-transition isunlikely to occur, thus making it harder to control furtherdepolarization caused by repetition of the lattice-distortion during thephase-transition. Therefore, this invention makes it possible to controltime-dependent deterioration of the piezoelectric property of thepiezoelectric-ceramic composition, thus improving the reliability ofthis electromechanical-transformation device.

The second aspect of this invention refers to theelectromechanical-transformation device according to first aspect ofthis invention, whereof the orthorhombic-to-tetragonal-phase transitiontemperature is within the range of the operating temperature of saiddevice and/or within the range of the storing temperature of saiddevice, and that the tetragonal-to-cubic-phase transition temperature iswithin the range higher than the operating temperature.

According to the second aspect of this invention, the temperature of theelectromechanical-transformation device varies during either use orstorage and exceeds the orthorhombic-to-tetragonal transitiontemperature or falls below said temperature. Even if such a variation intemperature should occur, the rigid body adhered to thepiezoelectric-ceramic composition makes phase-transition of the crystalstructures unlikely, thus controlling degradation of the piezoelectricproperty over time. Also, the temperature of the device will neverexceed the orthorhombic-to-cubic-transition temperature whilst thedevice is being used, thus making it possible to avoid loss of thepiezoelectric-ceramic composition due to further depolarization of saidcomposition.

The third aspect of this invention refers to anelectromechanical-transformation device, according to the first orsecond aspect of this invention, whereof a rigid body is adhered to thepiezoelectric-ceramic composition by a thermosetting resin-adhesive.

According to the third aspect of this invention, by using athermosetting resin-adhesive, heating the piezoelectric-ceramiccomposition to the curing temperature of said adhesive makes it possibleto adhere the rigid body whilst the piezoelectric-ceramic composition isin the state of a tetragonal-crystal structure. Such a rigid body makesthe tetragonal-to-orthorhombic phase transition of thepiezoelectric-ceramic composition unlikely, thus controlling furtherdepolarization of said composition.

The fourth aspect of this invention refers to theelectromechanical-transformation device, according to the first orsecond aspect of this invention, whereof the rigid body is adhered tothe piezoelectric-ceramic composition by an epoxide-based adhesive.

According to the fourth aspect of this invention, in using anepoxide-base adhesive, adhesion of the rigid body is suitably secured,and such an adhesive is stiff enough to transmit vibrations, so that theultrasonic vibrations of the electromechanical-transformation device isefficiently generated.

The fifth aspect of this invention refers to theelectromechanical-transformation device, according to the third orfourth aspect of this invention, whereof the adhesive that adheres therigid body to the piezoelectric-ceramic composition has a curingtemperature within the range exceeding theorthorhombic-to-tetragonal-phase transition temperature by 50 degreesCelsius or more and that is falls below the tetragonal-to-cubic-phasetransition temperature by 50 degrees Celsius or more.

According to the fifth aspect of this invention, heating thepiezoelectric-ceramic composition to the temperature at which saidcomposition becomes a tetragonal crystal, the adhesive hardens, and thusadhering the rigid body to said composition. The adhesive curingtemperature is lower than the tetragonal-to-cubic transitiontemperature, so that the crystal structure of the piezoelectric-ceramiccomposition does not become a cubic crystal whilst the rigid body isbeing adhered to said composition, thus preventing said composition frombeing depolarized. Even if the tetragonal-to-cubic transitiontemperature should become lower than the orthorhombic-to-tetragonaltransition temperature, whilst the electromechanical-transformationdevice is being used, the rigid body that is adhered to thepiezoelectric-ceramic composition makes the tetragonal-to-orthorhombicphase transition unlikely, thus preventing the piezoelectric property ofthe piezoelectric-ceramic composition from degrading over time.

The sixth aspect of this invention refers to theelectromechanical-transformation device, according to any one of thefirst to fifth aspects of this invention, whereof thepiezoelectric-ceramic composition is formulized as{Li_(x)(K_(1-y)Na_(y))_(1-x)}_(a)(Nb_(1-z-w)Ta_(z)Sb_(w))O₃ within thecomposition-range of 0.90≦a≦1.2, 0.02≦x≦0.2, 0.2≦y≦0.8, 0≦z≦0.5,0≦w≦0.2.

According to the sixth aspect of this invention, it is possible toobtain an alkali-niobate piezoelectric-ceramic composition of apreferable piezoelectric property at the Curie temperature of 340degrees Celsius or more and at the piezoelectric constant d₃₃ of 260pC/Nor more. The electromechanical-transformation device made of such apiezoelectric-ceramic composition fully secures product reliability.

The seventh aspect of this invention refers to theelectromechanical-transformation device, according to any one of thefirst to sixth aspects of this invention, whereof the rigid body is madeof a ceramic composition containing silica, alumina, or silica-aluminain major proportions.

According to the seventh aspect of this invention, it is possible toobtain a rigid body having a Young's modulus of 60 GPa or more. Also, inemitting ultrasonic sound waves from theelectromechanical-transformation device into a liquid, it is possible toapply the piezoelectric-ceramic composition of silica (SiO₂) or aluminain major proportions to the surface of theelectromechanical-transformation device to make it function as anacoustic-matching layer, thus improving the acoustic-radiationefficiency of the ultrasonic sound waves.

The eighth aspect of this invention refers to theelectromechanical-transformation device, according to any one of thefirst to seventh aspects of this invention, whereof thepiezoelectric-ceramic composition comprises a major surface acting as anacoustic-radiation surface, and that the rigid body that is adhered tothe acoustic-radiation surface of said composition acts as anacoustic-matching layer to emit ultrasonic waves, and that the thicknessof the rigid body is formulized as t={v/(4f)}±10% or t=[v/(2f)]±10% ofwhich f means the resonance-frequency of the piezoelectric-ceramiccomposition and v means the acoustic-velocity of the rigid body and tmeans the thickness of the rigid body.

According to the eighth aspect of this invention, thepiezoelectric-ceramic composition is formed in such a way that the rigidbody is adhered to the major surface that acts as an acoustic-radiationsurface, with the rigid body of thickness t corresponding to ½ or ¼ ofthe wavelength λ (=v/f) of the ultrasonic sound waves being emitted fromthe acoustic-radiation surface, thus enabling the rigid body to act asthe acoustic-matching layer, thus making it possible to emit saidultrasonic sound waves efficiently from theelectromechanical-transformation device, in which case it is unnecessaryto prepare the rigid body and acoustic-matching layer separately, thusreducing the cost of the components in making theelectromechanical-transformation device.

The ninth aspect of this invention refers to the method formanufacturing the electromechanical-transformation device, according toany one of the first to eighth aspects of the invention, with the methodcomprising a polarization-process in which a pair of electrodes isformed on the piezoelectric-ceramic composition, and in whichpolarization is provided on said composition by impressing a directcurrent of electricity between the electrodes; and comprising anadhesion-process in which the piezoelectric-ceramic composition and therigid body are adhered together by a thermosetting-adhesive of a curingtemperature-range exceeding the orthorhombic-to-tetragonal-phasetransition temperature by 50 degrees Celsius or more and falling belowthe tetragonal-to-cubic-phase transition temperature by 50 degreesCelsius or more, and that in the adhesion-process thethermosetting-adhesive is heated within the curing temperature-rangeafter completion of the foregoing polarization-process.

According to the ninth aspect of this invention, in thepolarization-process, a direct current of electricity is impressedbetween the pair of electrodes formed on the piezoelectric-ceramiccomposition to polarize said composition. Then, using thethermosetting-adhesive of a curing temperature-range exceeding theorthorhombic-to-tetragonal-phase transition temperature 50 degreesCelsius or more and falling below the orthorhombic-to-tetragonal-phasetransition temperature by 50 degrees Celsius or more, and by heating thepiezoelectric-ceramic composition within the curing temperature range,the thermosetting-adhesive hardens, thus causing the rigid body toadhere to the piezoelectric-ceramic composition. Such heating causes thecrystal structures of the piezoelectric-ceramic composition to become atetragonal crystal, thus adhering the rigid body to said composition,and in which case the temperature of theelectromechanical-transformation device becomes lower than theorthorhombic-to-tetragonal-phase transition-temperature, so that therigid body induces an external force to maintain lattice-distortion ofthe tetragonal crystal. As a result, the orthorhombic-to-tetragonalphase-transition of the piezoelectric-ceramic composition is unlikely tooccur, thus preventing depolarization of said composition. Therefore, itis possible to prevent the piezoelectric property of thepiezoelectric-ceramic composition from deteriorating over time, so thata highly reliable electromechanical-transformation device can bemanufactured.

Effects of the Invention

As described above, the first to eighth aspects of this inventionprovide an electromechanical-transformation device of which thepiezoelectric property is unlikely to deteriorate over time even ifchanges occur in the orthorhombic-to-tetragonal-phasetransition-temperature, and that the ninth aspect provides thepreferable method for manufacturing said device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is the oblique-perspective view of theelectromechanical-transformation device as the embodiment of thisinvention.

FIG. 2 is the cross-sectional view of theelectromechanical-transformation device as the embodiment of thisinvention.

FIG. 3 is a cross-sectional view of the skeleton framework of theultrasonic flow meter.

FIG. 4 illustrates the volume-ratio near the adhesion point of thepiezoelectric-ceramic composition as an embodiment of this invention.

FIG. 5 further illustrates the volume-ratio near the adhesion point ofthe piezoelectric-ceramic composition as an embodiment of thisinvention.

FIG. 6 further illustrates the volume-ratio near the adhesion point ofthe piezoelectric-ceramic composition as an embodiment of thisinvention.

FIG. 7 illustrates the adhesion-pattern of the rigid body as anembodiment of this invention.

FIG. 8 further illustrates the adhesion-pattern of the rigid body as anembodiment of this invention.

FIG. 9 further illustrates the adhesion-pattern of the rigid body as anembodiment of this invention.

FIG. 10 is another cross-sectional view of theelectromechanical-transformation device as the embodiment of thisinvention.

FIG. 11 is still another cross-sectional view of theelectromechanical-transformation device as the embodiment of thisinvention.

MODES FOR CARRYING OUT THE INVENTION

Hereinafter, the embodiments of the electromechanical-transformationdevice of this invention are described in reference to the figures.

FIG. 1 is the oblique-perspective view of theelectromechanical-transformation device 10 as the embodiment of thisinvention.

FIG. 2 is the cross-sectional view of the electromechanicaltransformation device 10. As shown in FIGS. 1 and 2, theelectromechanical-transformation device 10 comprises apiezoelectric-ceramic composition 11 and a rigid body 12 that is adheredto the piezoelectric-ceramic composition 11. Theelectromechanical-transformation device 10 of this invention is used asan ultrasonic sensor of the ultrasonic flow meter. (See FIG. 3)

The ultrasonic flow meter 15, as shown in FIG. 3, is provided on thechemical-solution circulating-line to measure the volume of thechemical-solution W1 flowing through the semiconductor-manufacturingequipment. The ultrasonic flow meter 15 consists of a U-shaped tube 16,17, with an electromechanical-transformation device 10 provided ateither edge of said tube, which transmits and receives ultrasonic wavesthrough the chemical solution W1, thereby measuring the velocity of saidsolution by the difference in time of the ultrasonic waves pulsing toand fro against the solution.

Of the embodiment of this invention, theelectromechanical-transformation device 10 comprises apiezoelectric-ceramic composition 11 consisting of a disk-shapedpotassium-sodium niobate-series (alkaline niobate-series) that is 10 mmin diameter, 1.4 mm thick, and has a Young's modulus of approximately100 GPa to 130 Gpa. The rigid body 12 of theelectromechanical-transformation device 10 is also disk-shaped, is madeof silica (SiO₂), is 10 mm in diameter and 0.7 mm thick, and, as anembodiment of this invention, is of a plate-like structure of the sameouter diameter as that of the piezoelectric-ceramic composition 11, butis thinner and has a Young modulus of 60 GPa and a linearexpansion-coefficient of 8 ppm/° C.

The piezoelectric-ceramic composition 11 comprises a first-majoracoustic-radiation surface 21 and a second-major rear surface 22, and apair of electrodes 23 and 24 (including the folded electrode 23 a)provided on said surfaces 21 and 22 of said composition 11, of which theelectrode 23 is provided on the first-major acoustic-radiation surface21 to which the rigid body 12 is adhered by the intermediary of theelectrode 23. Of the piezoelectric-ceramic composition 11, the foldedpart 23 a of the first electrode 23 (of the main acoustic-radiationsurface 21) and the second electrode 24 provided on the second rearsurface 22 are connected to the external wiring (signal wire 26 andground wire 27 as shown in FIG. 3). Of the second rear surface 22, theelectrodes 23 a and 24 are separated by the piezoelectric-ceramiccomposition 11 between them.

The rigid body 12 of the embodiment of this invention is adhered to theentire first-major surface 21 of the piezoelectric-ceramic composition11, which said surface 21 acts as an acoustic-radiation surface to emitultrasonic sound waves. The rigid body 12 is t (=0.7 mm) thick and isformed according to Formula (1): t={v/(4f)}±10% of which t means thethickness (=0.7 mm) and f means the resonance-frequency of thepiezoelectric-ceramic composition 11 and v means the sound-velocitywithin the rigid body 12.

The rigid body 12 is of thickness t, which is ¼ times that of theultrasonic wavelength λ(=v/f). The resonance-frequency of thepiezoelectric-ceramic composition 11 is 2 MHz, and the acoustic-velocityv within the rigid body 12 is approximately 5,600 m/s. Being of suchthickness t, the rigid body 12 acts as an acoustic-matching layer. Theadhesion-layer 13 between the piezoelectric-ceramic composition 11 andthe rigid body 12 is about tens of μ thick, which does not affect thepropagation of the ultrasonic wavelength λ(=v/f), which adhesion-layer13 is thinner than the rigid body 12. The adhesion layer 13 of thisembodiment is composed of for example a thermosetting epoxy-resin thatis cured at 150 degrees Celsius.

As shown in FIG. 3, the electromechanical-transformation device 10 ofthis invention is set within the chassis 18 of the ultrasonic flow meter15. The acoustic-radiation surface 21 (see FIG. 4) (of which is therigid body 12) is the acoustic-radiation surface and faces the U-shapedchemical-solution tube passage 16.

The piezoelectric-ceramic composition 11 comprises a crystal-phaseperovskite structure that is formed according to Formula (2):{Li_(x)(K_(1-y)Na_(y))_(1-x)}_(a)(Nb_(1-z-w)Ta_(z)Sb_(w))O₃.

This invention adopts the piezoelectric-ceramic composition 11 that isof the composition range of Formula (2): 0.90≦a≦1.2, 0.2≦x≦0.2,0.2≦y≦0.8, 0≦z≦0.5, 0≦w≦0.2. The electromechanical-transformation device10 of this embodiment comprises the piezoelectric-ceramic composition11, thus meeting the composition value of: a=0.98, x=0.04, y=0.54, z=0and w=0.04.

The piezoelectric-ceramic composition 11, according to Formula (2), hasa crystal structure, i.e. orthorhombic crystals, that is made at theside where the temperature is lower than theorthorhombic-to-tetragonal-phase transition temperature To-t, and hastetragonal crystals that are made at the side where the temperature ishigher than the orthorhombic-to-tetragonal-phase transition temperatureTo-t and at the side where the temperature is lower than thetetragonal-to-cubic-phase transition temperature Tc, and of has cubiccrystals that are made at the side where the temperature is higher thanthe tetragonal-to-cubic-phase transition temperature Tc. As anembodiment of this invention, the piezoelectric-ceramic composition 11has an orthorhombic-to-tetragonal-phase transition temperature To-t of30 degrees Celsius, a tetragonal-to-cubic-phase transition temperature(the Curie temperature) Tc of 345 degrees Celsius, and apiezoelectric-constant d₃₃ of 260pC/N.

Hereinafter, the method for manufacturing theelectromechanical-transformation device 10 is described.

First, prepare the base-powder (of 99% or more of purity of grade) ofK₂Co₃, Na₂CO₃, Li₂CO₃, Nb₂O₅, Ta₂O₅ and Sb₂O₃. According to Formula (2),to achieve a=0.98, x=0.04, y=0.54, z=0 and w=0.04, weigh the base-powdercontaining each metallic element. Then, using a ball-mill, mix thebase-power to get slurry. Next, soak the slurry in alcohol for 24 hours.The type of base-powder (compound) containing each metallic element isnot limited. An oxidized material, a carbonate or the like of eachmetallic element can be used.

Dry the slurry, obtained in the above process, and calcinate it at 900degrees Celsius for three hours. Using a ball-mill, crush the slurry for24 hours. Add a polyvinyl alcohol-water solution to the slurry andpelletize it. Then, press the pelletized powder under 20 MPa of pressureinto a disk 11.5 mm in diameter and 2.0 mm thick. Sinter the disk for2.5 hours at 1,000 to 1,200 degrees Celsius, which is the appropriatetemperature for obtaining a sintered body of maximum density.

Grind both surfaces of the sintered body simultaneously until it is adisk 10 mm in diameter and 1.4 mm thick. Apply the silver-paste(conductive-metal paste) onto both surfaces of the disk and heat thedisk at 700 degrees Celsius to form the electrodes 23, 24. In siliconeoil, apply a direct-current voltage of 3kV/mm to the electrodes 23, 24at 130 degrees Celsius for 20 minutes to achieve polarization in thedirection of thickness, thereby making the piezoelectric-ceramiccomposition 11 (Polarization Process).

Using the thermosetting-adhesive of a curing-temperature range of 50degrees Celsius higher than the orthorhombic-to-tetragonal-phasetransition temperature To-t (equal to 30 degrees Celsius), and 50degrees Celsius lower than the tetragonal-to-cubic transitiontemperature To (equal to 345 degrees Celsius), adhere the rigid body 12to the acoustic-radiation surface 21 of the piezoelectric-ceramiccomposition 11. Of the embodiment of this invention, the epoxy-seriesadhesive of a curing temperature of 150 degrees Celsius is thethermosetting resin-series adhesive. The adhesion-process involvesheating the epoxy-series adhesive to the curing temperature of 150degrees Celsius to adhere the rigid body 12 to the piezoelectric-ceramiccomposition 11, thus manufacturing the electromechanical-transformationdevice 10.

The inventors repeatedly tested the electromechanical-transformationdevice 10 for the effect of cooling and heating upon it to confirm thedeterioration of the piezoelectric property of said device 10 over time.The results of the test are shown in Chart 1.

Deterioration of the piezoelectric property over time was confirmed bythe following method. First, connect the wires 26 and 27 to theelectrodes 23, 24 of a pair of electromechanical-transformation devices10 that were manufactured by the above method. Then, set theelectromechanical-transformation devices 10 into the chassis 18 of theultrasonic flow meter 15, as shown in FIG. 3. Then, pass ultrasonicwaves between each device 10 and set the default transmission-receptionsensitivity (the voltage-value of the received signals) of saidultrasonic waves. Then, remove the electromechanical-transformationdevices 10 from the ultrasonic flow meter 15 and test the effect ofcooling and heating upon them by repeatedly cooling them at 20 degreesCelsius below zero for one hour 100 times and heating them to 200degrees Celsius for one hour 100 times. Then, again set theelectromechanical-transformation devices 10 into the chassis 18 of theultrasonic flow meter 15 and measure the transmission-receptionsensitivity. Now compare the decreasing rate (dB) of thetransmission-reception sensitivity of the ultrasonic waves after thecooling-heating-effect test with the default transmission-receptionsensitivity setting of the ultrasonic waves before thecooling-heating-effect test. The results are shown in Chart 1. WorkingExample 1, as shown in Chart 1, means that theelectromechanical-transformation device 10 was manufactured by the abovemethod.

The inventors manufactured the electromechanical-transformation device10 of Working Examples 2 to 6 and of Comparative Examples 1 to 7 bychanging the curing temperature of the adhesive to have it effectivelyadhere to the rigid body 12, changing the materials used in forming therigid body 12, changing the adhering position of the rigid body 12, andchanging the thickness of the piezoelectric-ceramic composition 10. Thecooling-heating-effect test was done on theelectromechanical-transformation device 10 to calculate the decreasingrate (dB) of the transmission-reception sensitivity of the ultrasonicwaves over time. The results are shown in Chart 1. Of the test, besidesa silica-based ceramics being used as the material for making the rigidbody 12, aluminum or polyether ether-ketone resin (PEEK) was used. TheYoung's modulus of aluminum is 70 GPa, and of the polyether ether-ketoneresin the Young's modulus is 4 GPa. Although not shown in Chart 1, thelinear-expansion coefficient of the aluminum and the polyetherether-ketone resin is 24 ppm/° C. and 45 ppm/° C. respectively.

CHART 1 Volume Adhesion substances Adhesive Decreasing ratio nearYoung's curing sensitivity Thickness Adhering adhesion modulustemperature Rate (mm) Adhesion position (%) Material (GPa) (° C.) (dB)Working 1.4 Yes Acoustic 100 Silica- 60 150 −0.2 Example 1 Radiationbased surface ceramics Comparative 1.4 Yes Acoustic 100 Silica- 60 60−2.3 Example 1 Radiation based surface ceramics Working 1.4 Yes Back 100Silica- 60 150 −0.1 Example 2 surface based ceramics Comparative 1.4 YesBack 100 Silica- 60 60 −2.4 Example 2 surface based ceramics Working 1.4Yes Back 100 Aluminum 70 150 −0.1 Example 3 surface Comparative 1.4 YesBack 100 Aluminum 70 60 −2.3 Example 3 surface Comparative 1.4 Yes Back100 PEEK 4 150 −0.9 Example 4 surface Comparative 1.4 Yes Back 100 PEEK4 60 −3.6 Example 5 surface Comparative 1.4 No — 0 — — — −4.2 Example 6Working 2 Yes Acoustic- 100 Silica- 60 150 −0.2 Example 4 Radiationbased surface ceramics Working 3 Yes Acoustic 67 Silica- 60 150 −0.3Example 5 Radiation based surface ceramics Working 5 Yes Acoustic 40Silica- 60 150 −0.4 Example 6 Radiation based surface ceramicsComparative 7 Yes Acoustic 29 Silica- 60 150 −0.6 Example 7 Radiationbased surface ceramics

The electromechanical-transformation device 10 of Working Example 2 isdifferent from that of Working Example 1, since the rigid body 12 isadhered to the back surface 22 of the piezoelectric-ceramic composition11. However, the other structures of said device 10 of Working Example 2are the same as those of Working Example 1. Also, theelectromechanical-transformation device 10 of Working Example 3 isdifferent from that of Working Example 1, since the rigid body 12 thatis adhered to the back surface 22 of the piezoelectric-ceramiccomposition 11 is made of aluminum. However, the other structures ofsaid device 10 of Working Example 3 are the same as those of WorkingExample 1. The electromechanical-transformation device 10 of WorkingExamples 4 to 6 is different from that of Working Example 1, since thethickness of the piezoelectric-ceramic composition 11 of said device 10of Working Examples 4 to 6 varies ranging from 2 to 5 mm. However, theother structures of said device 10 of Working Examples 4 to 6 are thesame as those of Working Example 1.

The electromechanical-transformation device 10 of Comparative Example 1is different from that of Working Example 1, since the curingtemperature of the adhesive used to adhere the rigid body 12 (theacoustic-matching layer) is changed to 60 degrees Celsius. However, theother structures of said device 10 are the same as those of WorkingExample 1. The electromechanical-transformation device 10 of ComparativeExample 2 is different from that of Working Example 2, since the curingtemperature of the adhesive is changed to 60 degrees Celsius. However,the other structures of said device 10 are the same as those of WorkingExample 2. The electromechanical-transformation device 10 of ComparativeExample 3 is different from that of Working Example 3, since the curingtemperature of the adhesive is changed to 60 degrees Celsius. However,the other structures of said device 10 are the same as those of WorkingExample 3.

The electromechanical-transformation device 10 of Comparative Example 4is different from that of Working Example 1, since the polyetherether-ketone resin (PEEK) is adhered to the back surface 22 of thepiezoelectric-ceramic composition 11. However, the other structures ofsaid device 10 are the same as those of Working Example 1. Theelectromechanical-transformation device 10 of Comparative Example 5 isdifferent from that of Comparative Example 4, since the curingtemperature of the adhesive is changed to 60 degrees Celsius. However,the other structures of said device 10 are the same as those ofComparative Example 4.

The electromechanical-transformation device 10 of Working Example 6 isdifferent from that of Working Example 1, since the rigid body 12 is notadhered. However, the other structures of said device 10 are the same asthose of Working Example 1. Regarding Comparative Example 6, grease mustbe applied between the acoustic-radiation surface 21 and the rigid body12 (acoustic-matching layer) of the piezoelectric-ceramic composition11, because the rigid body 12 is to be tightly set into the ultrasonicflow meter 15. Then, measure the transmission-reception sensitivity ofthe ultrasonic waves within the flow meter 15. Theelectromechanical-transformation device 10 of Comparative Example 7 isdifferent from that of Working Example 1, since the thickness of thepiezoelectric-ceramic composition 11 is changed to 7 mm. However, theother structures of said device 10 are the same as those of WorkingExample 1.

The volume-ratio near the adhesive, as shown in Chart 1, means thepercentage of volume of the piezoelectric-ceramic composition 11 withinthe range R1 (as described by the long-short dash-lines in FIGS. 4 and5) wherein the distance from the place (on the surface of the adhesivelayer 13) whereon the rigid body 12 is adhered to thepiezoelectric-ceramic composition 11 is 2 mm or less against the entirevolume of the piezoelectric-ceramic composition 11. Therefore, inadhering the rigid body 12 to the piezoelectric-ceramic composition 11of 2 mm thick or less (according to Working Examples 1 to 4 and ofComparative Examples 1 to 5), the entire volume of said composition 11is included within the range R1. Thus, the volume-ratio near theadhesive is 100%. (See FIG. 4)

If the piezoelectric-ceramic composition 11 is 2 mm thick or more, itpartially exceeds the range R1. Thus, the volume-ratio near the adhesionis smaller (see FIG. 5). Of the case of Working Example 5 of which therigid body 12 is adhered to the piezoelectric-ceramic composition 11that is 3 mm thick, the volume-ratio near the adhesion is 67%. In thecase of Working Example 5 of which the rigid body 12 is adhered to thepiezoelectric-ceramic composition 11 that is 5 mm thick, thevolume-ration near the adhesion is 40%. In the case of the ComparativeExample 7 of which the rigid body 12 is adhered to thepiezoelectric-ceramic composition 11 that is 7 mm thick, thevolume-ration near the adhesion is 29%. In case of Comparative Example 6of which the rigid body 12 is not adhered to the piezoelectric-ceramiccomposition 11, the volume-ration near the adhesion is 0%.

In the case of Working Examples 2 and 3 and of Comparative Examples 2 to5, of which the rigid body is adhered to the back surface 22, of theacoustic-radiation surface 21, of the piezoelectric-ceramic composition11, make the acoustic-matching layer out of the same material and of thesame shape as the rigid body 12 of Working Example 1 and adhering theacoustic-matching layer against the acoustic-radiation surface 21, ofthe piezoelectric-ceramic composition 11, using grease, to measure thetransmission-reception sensitivity of the ultrasonic waves. As such, theacoustic-matching layer gives the same measuring-condition as that ofthe Working Example 1, thus making it possible to correctly identify theadhesion effect of the rigid body 12.

As shown in Chart 1, regarding Working Examples 1 to 6, the rigid body12, (made of silica-based ceramics or of aluminum) and having a Young'smodulus of 60 GPa or more, is adhered to the surface of thepiezoelectric-ceramic composition 11 by heating said surface at 150degrees Celsius. Of Working Examples 1 to 6, the volume-ratio near theadhesion place of the piezoelectric-ceramic composition 11 is within therange R1 of which the distance from the place on the rigid body 12,being adhered to the piezoelectric-ceramic composition 11, is 2 mm orless thick, the volume-ratio is 40% or more. Thus, of Working Examples 1to 6, the decreasing-rate of the transmission-reception sensitivity ofthe ultrasonic waves, as shown by the cooling-heating-effect test, is0.4 dB to −0.1 dB (less than 5%), thus confirming that thepiezoelectric-ceramic composition 11 is less likely to deteriorate overtime. In the case of Working Examples 1 to 4 of which the volume-rationear the adhesion place, of the piezoelectric-ceramic composition 11 is100%, the decreasing-rate of the transmission-reception sensitivity ofthe ultrasonic waves is low, i.e., 0.2 dB to −0.1 dB, which makes itpossible to obtain a piezoelectric-ceramic composition 11 of which thepiezoelectric-property is less likely to deteriorate over time. In otherwords, regarding Working Examples 1 to 6, adhering the rigid body 12causes an external force in the direction where the lattice-distortionthat is induced by phase-transition is controlled. Thus, such aphase-transition is unlikely to occur. Thus, the progression ofdepolarization by repetition of the lattice-distortion is controlled,thus decreasing the piezoelectric-property degradation over time. Also,the adhesion place of the rigid body 12 is not only theacoustic-radiation surface 21 of the piezoelectric-ceramic composition11, but in the case of Working Examples 2 and 3 of which the rigid body12 is adhered to the back surface 22 of said composition 11, thedecreasing-rate of the transmission-reception sensitivity of theultrasonic waves is low, with the value being −0.1 dB, thus confirmingthat the piezoelectric-property of said composition 11 is unlikely todeteriorate over time.

In the case of Comparative Example 6 of which the rigid body 12 is notadhered to the piezoelectric-ceramic composition 11, repeating thephase-transition with changes in the temperature involving theorthorhombic-to-tetragonal-phase-transition temperature To-t, progressesthe depolarization of the piezoelectric-ceramic composition 11.Therefore, in the case of Comparative Example 6, the decreasing-rate ofthe transmission-reception sensitivity of the ultrasonic waves was shownto be −4.2 dB after the cooling-heating-effect test, meaning that thetransmission-reception sensitivity had decreased by about 40%. Also, itwas verified that as one of the properties of theelectromechanical-transformation device 10, the piezoelectric-constantd₃₃ that had been initially 260pC/N, decreased to 160pC/N, as shown bythe cooling-heating-effect test.

Regarding Comparative Examples 1 to 3 of which the curing temperature ofthe rigid body 12 is low (60 degrees Celsius), the adhesion of the rigidbody 12 to the piezoelectric ceramic composition 11 is of littleeffectiveness, and the decreasing-rate of the transmission-receptionsensitivity of the ultrasonic waves, as shown by thecooling-heating-effect test, is −2.3 dB (over 20%). RegardingComparative Examples 4 and 5 of which the polyether ether-ketone resinhaving a lower Young's modulus is adhered, the effectiveness of theadhesion is slight, and then the decreasing-rate of thetransmission-reception sensitivity of the ultrasonic waves is −0.9 dB orless (over 10%), thus showing time-degradation of the piezoelectricproperty. Regarding Comparative Example 7 of which thepiezoelectric-ceramic composition 11 is 7 mm thick, the volume-rationear the adhesion place is 29%. In other words, the volume-percentage ofthe piezoelectric-ceramic composition 11, which exceeds the range R1wherein the distance from the adhesion place of the rigid body 12, is 2mm or less, the volume-percentage increases to about 70%. Thus,regarding Comparative Example 7, the adhesion effect of the rigid body12 on the piezoelectric ceramic composition 11 cannot sufficiently beobtained as is shown by the decreasing-rate of thetransmission-reception sensitivity of the ultrasonic waves is being −0.6dB, thus confirming the degradation of the piezoelectric property.

Therefore, according to the embodiment of this invention, the followingeffect can be obtained.

(1) Of each piezoelectric-ceramic composition 11 of Working Examples 1to 6, the comparatively hard rigid body 12, having a Young's modulus of60 GPa or more is adhered to the acoustic-radiation surface 21 by theintermediary of the electrode 23, and that the adhesion of the rigidbody 12 is sufficiently secured such that the volume-ratio (near theadhesion) of the piezoelectric-ceramic composition 11 within the rangeof which the distance from the adhesion of the rigid body 12 is 2 mm orless, said volume-ratio should be 40% or more. As such, even if there isa change in temperature involving the orthorhombic-to-tetragonal-phasetransition temperature to-t, the rigid body 12 that is adhered to thepiezoelectric-ceramic composition 11 makes it unlikely that thecrystal-structural-phase transition (the tetragonal crystal changing tothe orthorhombic crystal) of the piezoelectric-ceramic composition 11will occur. Especially, if the thickness of the piezoelectric-ceramiccomposition 11, as the basis of the adhesion place with the saidcomposition 11 and the rigid body 12 is 2 mm or less (in case of WorkingExamples 1 to 4), the volume-ratio near the adhesion becomes 100%. Thus,such a rigid body 12 makes it possible to surely prevent thephase-transition of the piezoelectric-ceramic composition 11, thuspreventing time-degradation of the piezoelectric-property of thepiezoelectric-ceramic composition 11, which increasesproduct-reliability of the ultrasonic flow meter 15.

(2) The ultrasonic flow meter 15 that is used in the embodiment of thisinvention is provided on the chemical-solution circulating-line tomeasure the flow-volume of the chemical solution W1 being supplied tothe semiconductor-manufacturing equipment. Said flow meter 15 is used ina harsh environment in which the operating-temperature ranges from 0 to200 degrees Celsius. In other words, theorthorhombic-to-tetragonal-phase-transition temperature To-t (=30degrees Celsius) is within this operating-temperature range. Thus,whilst the ultrasonic flow meter 15 is being used, the temperature ofthe electromechanical-transformation device 10 exceeds or falls belowthe orthorhombic-to-tetragonal-phase-transition temperature To-t. Evenif there are is such a change in temperature, the rigid body 12 adheredto the piezoelectric-ceramic composition 11 makes it unlikely for thecrystal-structural-phase transition to occur, thus preventingdegradation of the piezoelectric-property of said composition 11 overtime. The tetragonal-to-cubic-phase transition temperature Tc (=345degrees Celsius) of the piezoelectric-ceramic composition 11 is within ahigher temperature-range than the operating-temperature limit of theultrasonic flow meter 15. In this case, the temperature of theelectromechanical-transformation device 10, whilst using the ultrasonicflow meter 15, will not rise to a higher temperature side than thetetragonal-to-cubic-phase transition temperature Tc, thus avoiding theprogression of depolarization of the piezoelectric-ceramic composition11, and thus maintaining a favorable piezoelectric-property. Therefore,the ultrasonic flow meter 15 of the embodiment of this invention makesit possible to correctly measure the flow-volume of the chemicalsolution W1.

(3) Regarding the electromechanical-transformation device 10 as theembodiment of this invention, the rigid body 12 is adhered to thepiezoelectric-ceramic composition 11 by an epoxy-series adhesive toachieve sufficient adhesiveness. The epoxy-series adhesive is ofappropriate stiffness for transmitting ultrasonic vibrations, thusmaking it possible for the electromechanical-transformation device 10 toemit ultrasonic vibrations efficiently.

(4) The embodiment of this invention has a high Curie temperature of 340degrees Celsius or more, thus imbuing the alkaline-niobate-seriespiezoelectric-ceramic composition 11 with a piezoelectric property thatis of a piezoelectric-constant 260pC/N or more. Therefore, theelectromechanical-transformation device 10 using such apiezoelectric-ceramic composition 11 allows for efficient transmissionand reception of ultrasonic sound waves, thus ensuringproduct-reliability of the ultrasonic flow meter 15. Also, thepiezoelectric-ceramic composition 11 is manufactured free of lead, thusavoiding harm to the environment in disposing of theelectromechanical-transformation device 10.

(5) Regarding Working Examples 1, 2 and 4 to 6, in using thesilica-based ceramic adhesive of silica (SiO2) as the main ingredient,it is possible to get a rigid body 12 having a Young's modulus of 60 GPaor more. Regarding Working Examples 1, 4 to 6, the rigid body 12 that isadhered to the acoustic-radiation surface 21 of thepiezoelectric-ceramic composition 11, is of thickness t corresponding toone fourth (¼) of the ultrasonic wavelength λ(=v/f) being emitted fromthe acoustic-radiation surface 21, thus letting the rigid body 12 act asan acoustic-matching layer, thus allowing for the ultrasonic waves to beemitted efficiently from the electromechanical-transformation device 10.It is thus unnecessary to prepare separately the rigid body 12 andacoustic-matching layer, thereby reducing the cost of components inmaking the electromechanical-transformation device 10.

(6) Regarding Working Example 3, in using aluminum adhesive, it ispossible to get a rigid body 12 having a Young's modulus of 70 GPa.Also, since aluminum is a comparatively light metal, the weight of theelectromechanical-transformation device 10 and rigid body 12 is reduced.

(7) The epoxy-series adhesive that is used as an embodiment of thisinvention has a curing temperature (of 150 degrees Celsius), which ishigher than the orthorhombic-to-tetragonal-phase transition temperatureTo-t by 50 degrees Celsius or more, and lower than thetetragonal-to-cubic phase transition temperature Tc by 50 degreesCelsius. The rigid body 12 is adhered to the piezoelectric-ceramiccomposition 11 within the temperature range—specifically at 150 degreesCelsius at which temperature the crystal structure of said composition11 is a tetragonal crystal—that is higher than theorthorhombic-to-tetragonal-phase transition temperature To-t by 50degrees Celsius or more, and lower than the tetragonal-to-cubic phasetransition temperature Tc by 50 degrees Celsius. As such, the adhesionof the rigid body 12 to said composition 11 does not bring thetetragonal-crystal-phase transition to the crystal structures, thuspreventing the progression of depolarization of said composition 11.Even if the temperature becomes lower than theorthorhombic-to-tetragonal-phase transition temperature To-t, the rigidbody 12 works an external force to maintain the lattice-distortion ofthe tetragonal crystal, thus making it unlikely that the tetragonalcrystal will change into a orthorhombic crystal, and thus preventingtime-degradation of the piezoelectric property of thepiezoelectric-ceramic composition 11.

(8) Of the embodiment of this invention, the rigid body 12 comprisingthe electromechanical-transformation device 10 is thinner than thepiezoelectric-ceramic composition 11, and the adhesive 13 that adheressaid rigid body 12 to said composition 11 is thinner than the rigid body12, which makes it possible to make said device 10 more compactly andthinner, thereby letting it easily to be set into the chassis 18 of theultrasonic flow meter 15 of the electromechanical-transformation device10. If the layer of the adhesive 13 is too thick, it works as a dampingmaterial (buffer), lowering the sensitivity of theelectromechanical-transformation device 10. Since the stiffness of theadhesive 13 is lower than that of the rigid body 12, the layer ofadhesive 13 that is too thick decreases the effect in controlling thelattice-distortion caused by the phase-transition, thus resulting indegradation of the piezoelectric-property of the piezoelectric-ceramiccomposition 11 over time. Contrarily, the embodiment of this inventionadopts an adhesive layer 13 of tens of μm thick, which does notadversely affect the propagation of the ultrasonic waves, thus surelyavoiding the sensitivity-degradation of theelectromechanical-transformation device 10.

The embodiment of this invention can be modified, as follows.

Of the embodiment of this invention, as described above, the rigid body12 is formed such that the following formula is established:t={v/(4f)}±10% (t=thickness of the rigid body 12, f=resonance frequencyof the piezoelectric-ceramic composition 11, v=acoustic velocity withinthe rigid body 12). However, it is possible to form the rigid body 12 tomeet the condition of formula t={v/(2f)}±10%. In other words, it ispossible to form the rigid body 12 of a thickness that is ½ times thatof the ultrasonic wavelength λ. This enables the rigid body 12 to act asan acoustic-matching layer, thus efficiently emitting ultrasonic wavesfrom the piezoelectric-ceramic composition 11 by the intermediary of therigid body 12, in which case the thickness t of the rigid body 12 istwice that of the aforementioned embodiment. Theelectromechanical-transformation device 10 of the embodiment, asdescribed above, adopts the rigid body 12 of a smaller thickness thanthat of the piezoelectric-ceramic composition 11. However, it ispossible to adhere the rigid body 12 of a larger thickness than that ofthe piezoelectric-ceramic composition 11 in making theelectromechanical-transformation device 10. However, if the thickness ofthe rigid body 12 is too large, the oscillatory-load will become tooheavy. Contrarily, if the thickness of the rigid body 12 is too small,its strength will be insufficient, thus losing its effect, which wouldmake it difficult for the phase-transition to occur. Thus, it is betterto form the rigid body 12 according to the appropriate thickness t andin consideration of the strength or the oscillatory of theformation-materials of the rigid body 12, as well as theresonance-frequency of the piezoelectric-ceramic composition 11 and ofthe acoustic-velocity v within the rigid body 12.

Of the electromechanical-transformation device 10 of the embodiment, asdescribed above, the rigid body 12 adhered to the piezoelectric-ceramiccomposition 11 is disk-shaped, but it is not limited to beingdisk-shaped. The rigid body 12, for example, can be a frame-shaped(ring-shaped) body having a hole in the center, or it is as alattice-shaped body having multiple holes. Also, besides acircular-rigid body, it is possible to adopt other shapes such as atriangle, a square or a polygonal, in which case there are some areas onthe adhesion surface (the first-major surface 21 (acoustic-radiationsurface 21) or on the second-major surface 22) (the back surface 22) ofthe piezoelectric-ceramic composition 11 to be formed, on which therigid body 12 is not adhered. Even in this case, the rigid body 12should be adhered such that the volume-ratio near the adhesion place ofthe piezoelectric-ceramic composition 11 is 40% or more.

FIG. 6 shows the embodiment of the electromechanical-transformationdevice 10A on which the lattice-shaped rigid body 12A is adhered to thefirst-major surface 21 (acoustic-radiation surface 21) of thepiezoelectric-ceramic composition 11. Also shown in FIG. 6 is the rigidbody 12A being of a specific size and of the lattice intervals adhered(to said composition 11) such that the volume-percentage (volume-rationear the adhesion place) of the piezoelectric-ceramic composition 11,being within the range R1 (shown by the long-and-short dash-lines) wherethe distance from the adhesion point place of the piezoelectric-ceramiccomposition 11 and of the rigid body 12A is 2 mm or less, is 40% ormore. In this case where the lattice-shaped rigid body 12A is beingused, it is better to set the width of the gap of the lattice of therigid body 12A at 2 mm or less, thus making it possible to secure theproper volume-ratio near the adhesion place of the piezoelectric-ceramiccomposition 11. Such an adhesion-effect of the rigid body 12A preventsthe piezoelectric property of the piezoelectric-ceramic composition 11from degrading over time.

Of the electromechanical-transformation device 10 of the embodiment asdescribed above, the adhesive 13 is provided on the entire interface ofthe piezoelectric-ceramic composition 11 and the rigid body 12, toadhere the rigid body 12 to said composition 11, but a differentformation-pattern can be used. The formation-pattern of the adhesive 13formed on the interface of the piezoelectric-ceramic composition 11 andthe rigid body 12 can also be a lattice as shown in FIG. 7 or lines asshown in FIG. 8 or dots as shown in FIG. 9. When adopting one of theadhesion-patterns as shown in FIGS. 7 to 9, the rigid body 12 is adheredaccording to the interval and width of the pattern such that thevolume-ratio near the adhesion place is 40% or more. In the adhesionprocess, the rigid body 12 can also be adhered to thepiezoelectric-ceramic composition 11 after applying the adhesive 13 tothe surface of the rigid body 12 or after applying it to the surface ofthe piezoelectric-ceramic composition 11.

Of the electromechanical-transformation device 10 of the embodiment asdescribed above, the rigid body 12 is formed of the silica-basedceramics whilst being adhered to the first-major surface 21(acoustic-radiation 21) (in the case of Working Examples 1 and 4 to 6),or it is formed of the silica-based ceramics or of aluminum whilst therigid body 12 is being adhered onto the second-major surface 22 (backsurface 22), in the case of Working Examples 2 and 3. The rigid body 12is not limited to being made of a silica-based ceramics or of aluminumbut of other materials having a Young's modulus of 60 GPa or more.Specifically, the rigid body 12 to be adhered to the first-major surface21 and to the second-major surface 22 includes a rigid body 12containing not only silica but aluminum or silica-alumina as the majoringredient. The rigid body 12 to be adhered to the second-major surface22 includes not only aluminum but also copper or stainless steel or thelike.

Of the electromechanical-transformation device 10 of the embodiment asdescribed above, the piezoelectric-ceramic composition 11 isdisk-shaped. The first-major surface 21 or the second-major surface 22to be adhered to the rigid body 12 is flat but is not necessarily so,for it is possible to provide a mesh-like slit (groove portion) oneither the first-major surface 21 or the second-major surface 22 of thepiezoelectric-ceramic composition 11. The slit formed on the surface ofsaid composition 11 allows for greater flexibility transversely, thusimproving the piezoelectric property of said composition 11. As such,the electromechanical-transformation device 10 is made by adhering therigid body 12 to the piezoelectric-ceramic composition 11 having asurface whereof the slit 31 is formed or is not formed. Regarding thepiezoelectric ceramic-composition 11A as shown in FIG. 10, whilstadhering the rigid body 12 to the surface 21 whereon the slit 31 isformed, an air-gap is formed on the concave portion of the slit 31, inwhich case it is possible to insert an elastic material such as rubberor the like into the concave portion. As shown in FIG. 11, it is alsopossible to insert a hard material 32 such as an epoxy-resin into theconcave portion of the slit 31, thus preventing the air-gap from formingbetween the rigid body 12 and the piezoelectric-ceramic composition 11A.As such, an acoustic-impedance of the electromechanical-transformationdevice 10 (an ultrasonic-transducer) changes to allow for a moreefficient acoustic-coupling, thus allowing a reinforcing-effect of thepiezoelectric-ceramic composition 11A, thus maintaining the adhesivenessof the piezoelectric-ceramic composition 11A and of the hard material 32as a filler. Using the hard material 32 having a Young's modulus of 60GPa or more makes it possible to control the lattice-distortionoccurring during the phase-transition of the piezoelectric-ceramiccomposition 11A.

Of the embodiment as described above, it is possible to set thepiezoelectric-ceramic composition 11 into the chassis 18 or into asensor-mounting holder or the like that comprises the ultrasonic flowmeter 15, so that such the chassis 18 or holder or the like can act as athe rigid body. In this case, it is necessary to use a material having aYoung's modulus of 60 GPa or more.

Of the electromechanical-transformation device 10 as the embodiment asdescribed above, the rigid body 12 is adhered to thepiezoelectric-ceramic composition 11 by a thermosetting resin-seriesadhesive such as an epoxy-series adhesive. However, the type of adhesivecan be changed. Beside an epoxy-resin type, a polyimide-resin adhesivecan be used or a thermoplastic adhesive or light-curing adhesive can beused. Moreover, when the rigid body 12 is formed in using a material ofhigh soderability, solder can be used as the adhesive. It is alsopossible to form the rigid body 12 by incorporating the adhesiveingredient and by heating it until the adherence-property expresses onthe surface of the rigid body 12, thus making it possible to adhere therigid body 12 to the piezoelectric-ceramic composition 11.

Of the electromechanical-transformation device 10 as the embodiment asdescribed above, the rigid body 12 is adhered to thepiezoelectric-ceramic composition 11 by attaching the electrodes 23, 24to the major surfaces 21 and 22 of the piezoelectric-ceramic composition11, yet those surfaces are not the only ones available. For example,when forming the rigid body 12 using an electrical-conducting materialsuch as metal or the like, it is possible to directly adhere the rigidbody 12 (now acting as an electrode) to the major surfaces 21 and 22 ofthe piezoelectric-ceramic composition 11, thus forming theelectromechanical-transformation device 10. Whilst forming thethick-type of the piezoelectric-ceramic composition 11, the rigid body12 can be adhered directly to a side-surface of said device 10 on whichthe electrodes 23, 24 have not been formed.

Of the embodiment as described above, it is possible to add the metallicelements Bi, Fe or the like to the piezoelectric-ceramic composition 11,thus making said composition 11 having a favorable piezoelectricproperty.

Of the embodiment as described above, theelectromechanical-transformation device 10 is used as anultrasonic-sensor of the ultrasonic flow meter 15, but the said device10 is not limited to that use. For example, it can be used as anair-bubble detection-sensor to measure the decreasing rate of theultrasonic waves propagating against the circulating chemical solutionand to detect the existence or non-existence of the bubbles based on thea decreasing rate of the ultrasonic waves. Also, the said device 10 canbe used as an ultrasonic-concentration meter to detect the concentrationof the circulating chemical solution based on the decreasing rate of theultrasonic waves. Also, the said device 10 can be used as aknocking-sensor or actuator in an engine, in an ultrasonic-transducer orin an ultrasonic washing machine or the like. Finally, theelectromechanical-transformation device 10 is disk-shaped. However, theshape or size of said device 10 can be changed according to the intendeduse.

Besides the technical ideas of this invention as described above, thetechnical ideas as described hereinafter are to be understood.

-   (1) An electromechanical-transformation device according to any one    of the first to eighth aspects of this invention is characterized in    that the volume-percentage of the piezoelectric-ceramic composition    is within the range in which the distance from the adhesion place of    said composition and the rigid body is 2 mm or less, and that the    percentage of volume against the whole volume of the    piezoelectric-ceramic composition is 45% or more.-   (2) An electromechanical-transformation device according to any one    of the first to eighth aspects of this invention is characterized in    that the Young's modulus of the rigid body is 65 GPa or more.-   (3) An electromechanical-transformation device according to any one    of the first to eighth aspects of this invention is characterized by    the Young's modulus of the rigid body being from 65 GPa to 80 GPa.-   (4) An electromechanical-transformation device according to any one    of the first to eighth aspects of this invention is characterized in    that the linear-expansion coefficient of the rigid body is 24    ppm/° C. or less.-   (5) An electromechanical-transformation device according to any one    of the first to eighth aspects of this invention is characterized in    that the linear-expansion coefficient of the rigid body is from 7    ppm/° C. to 24 ppm/° C.-   (6) An electromechanical-transformation device according to any one    of the first to eighth aspects of this invention is characterized in    that the thickness of the rigid body is smaller than that of the    piezoelectric-ceramic composition, and that the thickness of the    adhesive that is used in adhering the rigid body to said composition    is smaller than that of the rigid body.-   (7) An electromechanical-transformation device according to any one    of the first to eighth aspects of this invention is characterized in    that the thickness of the rigid body is smaller than that of the    piezoelectric-ceramic composition, and that the thickness of the    adhesive that is used in adhering the electrode and rigid body to    said composition is smaller than that of the rigid body.-   (8) An electromechanical-transformation device according to any one    of the first to eighth aspects of this invention is characterized in    that the electrode is formed by heating the conductive metal-paste.-   (9) An electromechanical-transformation device according to any one    of the first to eighth aspects of this invention is characterized in    that the piezoelectric-ceramic composition is lead-free.-   (10) An electromechanical-transformation device according to any one    of the first to eighth aspects of this invention is characterized in    that the piezoelectric-ceramic composition is an alkaline-niobate    series-ceramic composition having a crystal phase of a perovskite    structure.-   (11) An electromechanical-transformation device according to any one    of the first to eighth aspects of this invention is characterized in    that the thickness of the piezoelectric-ceramic composition—as the    standard of the adhesion of the piezoelectric-ceramic composition 11    and the rigid body 12—is 2 mm or less.-   (12) An electromechanical-transformation device according to any one    of the first to eighth aspects of this invention is characterized in    that the piezoelectric-ceramic composition is formed in the shape of    a plate comprising the first-major surface and second-major surface,    and that the rigid body is plate-like and of the same size or larger    than that of the outer-diameter of the piezoelectric-ceramic    composition to be adhered onto the entire first-major surface and    second-major surface of said composition.-   (13) An electromechanical-transformation device according to any one    of the first to eighth aspects of this invention is characterized in    that the piezoelectric-ceramic composition is formed into the shape    of a plate comprising the first-major surface as an    acoustic-radiation surface and the second-major surface as the back    of the acoustic-radiation surface.-   (14) An electromechanical-transformation device according to any one    of the first to eighth aspects of this invention is characterized in    that the orthorhombic-to-tetragonal-phase transition temperature is    within 0 to 100 degrees Celsius, and that the curing temperature of    the adhesive is 150 degrees Celsius.-   (15) An electromechanical-transformation device, according to the    third or fourth aspect of this invention, is characterized in that    the adhesive comprises a thermosetting epoxy-resin that is cured at    a temperature exceeding 100 degrees or more than the    orthorhombic-to-tetragonal-phase transition temperature.-   (16) An electromechanical-transformation device according to any one    of the first to eighth aspects of this invention is characterized in    that said device is set in a place that is heated to 100 degrees    Celsius or more when in use.-   (17) An electromechanical-transformation device, according to any    one of the first to eighth aspects of this invention, is    characterized in that said device is set into the ultrasonic flow    meter to measure the volume of flow of the chemical solution being    supplied to the semiconductor-manufacturing equipment.-   (18) An electromechanical-transformation device, according to any    one of the first to eighth aspects of this invention, is    characterized in that said device is used as an ultrasonic sensor to    transmit and receive ultrasonic waves, and that after 100 cycles of    a thermal-effect test that was done within a temperature-range that    is lower and higher than the orthorhombic-to-tetragonal-phase    transition temperature, the decreasing-rate of the    transmission-reception sensitivity was found to be 5% or less than    the default value set before the thermal-effect test.-   10, 10A: Electromechanical-transformation device-   11, 11A: Piezoelectric-ceramic composition-   12, 12A: Rigid body-   21: First-major surface (Acoustic-radiation surface) as the main    surface-   22: Second-major surface (Back surface) as the main surface-   23, 24: Electrode-   R1: Range less than 2 mm-   To-t: Orthorhombic-to-tetragonal-phase transition temperature-   Tc: Tetragonal-to-cubic-phase transition temperature

1. An electromechanical-transformation device using crystal structuresthat include an orthorhombic crystal formed at the side where thetemperature is lower than the orthorhombic-to-tetragonal-phasetransition temperature and that include a tetragonal crystal formed atthe side where the temperature is higher than theorthorhombic-to-tetragonal-phase transition temperature and at the sidewhere the temperature is lower than the tetragonal-to-cubic-phasetransition temperature and that include a cubic crystal formed at theside where the temperature is higher than the tetragonal-to-cubic-phasetransition temperature, and wherein that theelectromechanical-transformation device comprises a rigid body having aYoung's modulus of 60 GPa or more and comprises a piezoelectric-ceramiccomposition of which a volume-percentage, being within the range ofwhich the distance from the point of attachment of the rigid body to thepiezoelectric-ceramic composition is two mm or less, is 40% or more ascompared to the whole piezoelectric-ceramic composition and thepiezoelectric-ceramic composition has a major surface acting as anacoustic radiation surface, that the rigid body is directly adhered tothe major surface of a piezoelectric-ceramic composition or indirectlyto the major surface by the intermediary electrodes and acts as anacoustic-matching layer to emit ultrasonic waves, and that the thicknessof the rigid body is formulized as t={v/(4f)}±10% or t=[v/(2f)]±10% ofwhich f means the resonance-frequency of the piezoelectric-ceramiccomposition and v means the acoustic-velocity of the rigid body and tmeans the thickness of the rigid body.
 2. Anelectromechanical-transformation device according to claim 1, whereofthe orthorhombic-to-tetragonal-phase transition temperature is withinthe range of the operating temperature of said device and/or within therange of the storing temperature of said device, and that thetetragonal-to-cubic-phase transition temperature is within a temperaturerange higher than the operating temperature.
 3. Anelectromechanical-transformation device, according to claim 1, whereof arigid body is adhered to the piezoelectric-ceramic composition by athermosetting resin-adhesive.
 4. An electromechanical-transformationdevice, according to claim 1, whereof the rigid body is adhered to thepiezoelectric-ceramic composition by an epoxide-based adhesive.
 5. Anelectromechanical-transformation device, according to claim 3, whereofthe adhesive that adheres the rigid body to the piezoelectric-ceramiccomposition has a curing temperature within the range exceeding theorthorhombic-to-tetragonal-phase transition temperature by 50 degreesCelsius or more and that is falls below the tetragonal-to-cubic-phasetransition temperature by 50 degrees Celsius or more.
 6. Anelectromechanical-transformation device, according to claim 1, whereofthe piezoelectric-ceramic composition is formulized as{Li_(x)(K_(1-y)Na_(y))_(1-x)}_(a)(Nb_(1-z-w)Ta_(z)Sb_(w))O₃ within thecomposition-range of 0.90≦a≦1.2, 0.02≦x≦0.2, 0.2≦y≦0.8, 0≦z≦0.5,0≦w≦0.2.
 7. An electromechanical-transformation device, according toclaim 1, whereof the rigid body is made of a ceramic compositioncontaining silica, alumina, or silica-alumina in major proportions. 8.(canceled)
 9. A method for manufacturing theelectromechanical-transformation device, according to claim 1, with themethod comprising a polarization-process in which a pair of electrodesis formed on the piezoelectric-ceramic composition, and in whichpolarization is provided on said composition by impressing a directcurrent of electricity between the electrodes; and comprising anadhesion-process in which the piezoelectric-ceramic composition and therigid body are adhered together by a thermosetting-adhesive of a curingtemperature-range exceeding the orthorhombic-to-tetragonal-phasetransition temperature by 50 degrees Celsius or more and falling belowthe tetragonal-to-cubic-phase transition temperature by 50 degreesCelsius or more, and that in the adhesion-process thethermosetting-adhesive is heated within the curing temperature-rangeafter completion of the foregoing polarization-process.